linux-kernel - Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel

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Date:   Thu, 2 Aug 2018 17:00:25 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        linux-doc@...r.kernel.org, Will Deacon <will.deacon@....com>,
        Kostya Serebryany <kcc@...gle.com>,
        linux-kselftest@...r.kernel.org,
        Chintan Pandya <cpandya@...eaurora.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        linux-arch@...r.kernel.org, Jacob Bramley <Jacob.Bramley@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lee Smith <Lee.Smith@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel

On Wed, Aug 1, 2018 at 7:42 PM, Catalin Marinas <catalin.marinas@....com> wrote:
> On Mon, Jul 16, 2018 at 01:25:59PM +0200, Andrey Konovalov wrote:
>> On Thu, Jun 28, 2018 at 9:30 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
>> So the checker reports ~100 different places where a __user pointer
>> being casted. I've looked through them and found 3 places where we
>> need to add untagging. Source code lines below come from 4.18-rc2+
>> (6f0d349d).
> [...]
>> I'll add the 3 patches with fixes to v5 of this patchset.
>
> Thanks for investigating. You can fix those three places in your code

OK, will do.

> but I was rather looking for a way to check such casting in the future
> for newly added code. While for the khwasan we can assume it's a debug
> option, the tagged user pointers are ABI and we need to keep it stable.
>
> We could we actually add some macros for explicit conversion between
> __user ptr and long and silence the warning there (I guess this would
> work better for sparse). We can then detect new ptr to long casts as
> they appear. I just hope that's not too intrusive.
>
> (I haven't tried the sparse patch yet, hopefully sometime this week)

Haven't look at that sparse patch yet myself, but sounds doable.
Should these macros go into this patchset or should they go
separately?